Our DNA harbours a biological clock that can help
predict how long a person will live, research suggests.

That biological clock is a kind of chemical change -
methylation - that happens in DNA over time. Methylation is an epigenetic change, meaning that it does not alter the DNA code but rather influences
whether genes will be switched on or off.

By analysing different patterns of methylation
scientists can estimate a person's 'biological age'.

Four independent studies
tracked the lives of 5,000 people for up to 14 years and compared biological
age of blood samples with chronological age. The researchers found that a faster-running biological clock was linked with an earlier death.

The result held true even after adjusting for other
factors like smoking, diabetes and cardiovascular disease. Even after
accounting for these and other variables, people whose biological age was five
years more than their actual age were 16 percent more likely to die during the
period they were tracked.

Professor Ian Deary, of the University of Edinburgh,
a senior author of the study, said the research team had 'identified a novel
indicator of ageing, which improves the prediction of lifespan over and above
the contribution of factors such as smoking, diabetes, and cardiovascular
disease.'

Future research hopes to explain what is behind differences
in methylation patterns.

'At present, it is not clear what
lifestyle or genetic factors influence a person's biological age,' said Dr Riccardo Marioni, also from the University of Edinburgh.

'There is an ongoing project now to
try to narrow down the effects of the precise relationship of biological clocks
and mortality risks and what the other influences are,' he told the Daily
Express.

Scientists are still searching for a key piece of the longevity puzzle, having not found anything remarkable in the genes of 'supercentenarians' - people who live beyond 110 - to explain their long lives...

Analysis of person's DNA when they are still young could provide important clues about how long they will live, if a study on zebra finches is anything to go by. Research shows that the best indicator of the birds' longevity is the length of a section of genetic code at the end of their chromosomes, called the telomere...